As semiconductor devices have become more highly integrated, there has been a demand for a high yield of the semiconductor devices in a semiconductor fabricating process as well as a demand for a high integration. Particularly, in order to achieve a high yield, a surface of a substrate such as a semiconductor wafer is required to be highly clean, and thus a demand for clarification has been increasing. Under such a circumstance, a surface of a substrate is cleaned by a variety of cleaning processes in the semiconductor fabricating process. In recent years, there has been a tendency to use a low-k film (a low dielectric film) in order to lower a dielectric constant of an insulating film. Since a surface of the low-k film exhibits hydrophobicity, the number of processes for cleaning a substrate having a hydrophobic surface tends to increase.
In the semiconductor fabricating process, as a diameter of a semiconductor wafer becomes large, a single wafer processing apparatus is being introduced in an increasing number of wet processes. A spin-type processing apparatus is widely known as the single wafer processing apparatus for use in a wet process, and is applied to a cleaning apparatus and a drying apparatus for a semiconductor wafer.
The above-mentioned spin-type processing apparatus is operated as follows: A substrate is rotated at a high speed by a substrate holder such as a spin chuck, and a chemical liquid is supplied to the substrate, which is being rotated, to clean the substrate. Thereafter, a cleaning liquid such as ultrapure water is supplied to wash out the chemical liquid, and then the substrate is rotated at a higher speed to remove the cleaning liquid, so that the substrate is dried.
However, in the conventional processing apparatus described above, the liquid such as the cleaning liquid is likely to remain on a portion of the substrate near the substrate holder, and hence the liquid being present near the substrate holder is not quickly replaced with a new liquid. The liquid is also likely to be scattered from the substrate holder to cause contamination of the substrate.
In a spin dry apparatus for drying a substrate by rotating the substrate at a high speed, a large amount of mist is scattered due to the high rotation, and hence water marks are produced on a surface of a substrate. In this spin dry apparatus, although a peripheral portion of the substrate is quickly dried, a liquid on an undried area located at a central portion of the substrate tends to adhere to a dried area, i.e., the peripheral portion. Further, the liquid, which has been scattered from the peripheral portion of the substrate, bounces off a wall surface of a chamber (a processing room) and then adheres to the surface of the substrate again, thus causing the water marks. Furthermore, the central portion of the substrate cannot be dried sufficiently because a centrifugal force does not act on the central portion. In a case where the substrate is held by the substrate holder such as a spin chuck, a portion of the substrate near the substrate holder is not sufficiently dried, and hence a long processing time is required to dry the substrate.
On the other hand, it has been attempted to supply a gas from a gas supply unit to a substrate so as to dry the substrate while rotating the substrate at a high speed by a substrate holder. However, since the substrate holder such as a spin chuck, which can rotate the substrate at a high speed, is disposed underneath the substrate, it is difficult to equally dry an upper surface and a lower surface of the substrate with the gas. Specifically, when the gas is supplied to the lower surface of the substrate, it is difficult to dry the substrate without producing the water marks on the lower surface of the substrate. As described heretofore, since the conventional spin dry apparatus removes a liquid such as a cleaning liquid or a rinsing liquid from the substrate by utilizing a centrifugal force, it is difficult to dry the substrate without rotating the substrate at a high speed.
Further, as a low-k film is used as an insulating film, the following problems arise: When a wet process such as a chemical liquid process or a rinsing process is performed on a surface, which includes a hydrophobic surface, of a substrate, the entire surface of the substrate is not covered with a processing liquid such as a chemical liquid or a rinsing liquid, and hence the hydrophobic surface is exposed at the surface of the substrate. In this state, if the substrate is processed, a part of the processing liquid adheres to the hydrophobic surface in the form of a droplet and this droplet is moved on the hydrophobic surface to produce water mark on a trace of the moved droplet. Further, when the substrate is rotated at a high speed so as to dry the substrate, the droplet of the processing liquid is thrown off from the substrate and impinges on a wall surface of a chamber or the substrate holder, and then adheres again to the surface of the substrate. This droplet of the processing liquid is moved on the surface of the substrate as the substrate is rotated, and hence the water mark is produced on the trace of the moved droplet. Such water mark causes a reduction of the yield of products.
In the conventional spin-type processing apparatus, the chemical liquid process is performed while some portions of a substrate are clamp portioned by the substrate holder. Accordingly, it is hard to process such portions with the chemical liquid, and hence metal, which serves as an interconnect material, remains on these portions to cause metal contamination, resulting in lowering of reliability of the products.
The conventional spin-type processing apparatus is also problematic in terms of a uniform process over the entire surface of the substrate because the liquid is supplied only to one portion such as a central portion of the substrate and spreads over the entire surface of the substrate by the rotation of the substrate.
In recent years, a substrate holding apparatus having a plurality of rollers for holding and rotating a substrate has been used in a semiconductor fabricating apparatus such as a cleaning apparatus or an etching apparatus. FIG. 37 is a plan view schematically showing a conventional substrate holding apparatus for use in a cleaning process or an etching process. As shown in FIG. 37, the substrate holding apparatus comprises rollers 450a, 450b, 450c and 450d (hereinafter collectively referred to as rollers 450) for holding a semiconductor wafer W horizontally and rotating the semiconductor wafer W. The respective rollers 450 are moved in parallel with each other in directions indicated by arrows in FIG. 37 and rotated by motors serving as drive sources (not shown). When the semiconductor wafer W is transferred to the substrate holding apparatus, the four rollers 450 are moved toward the semiconductor wafer W to be brought into close contact with an edge portion of the semiconductor wafer W. The semiconductor wafer W is thus held by being held in close contact with the rollers 450. While holding the semiconductor wafer W, the rollers 450 are rotated by the motors, whereby the semiconductor wafer W is rotated.
However, in the conventional substrate holding apparatus shown in FIG. 37, the rollers 450 are not disposed at equal intervals along the edge portion of the semiconductor wafer W, and are moved in parallel with each other so as to be brought into close contact with the edge portion of the semiconductor wafer W. Therefore, a resultant of pressing forces applied from the rollers 450 to the semiconductor wafer W does not become zero at a central portion of the semiconductor wafer W. Accordingly, when the semiconductor wafer W is held and rotated by the rollers 450, stability of a position of a rotational center of the semiconductor wafer W is worsened. Further, contact positions between the rollers 450 and the edge portion of the semiconductor wafer W vary upwardly and downwardly while the substrate is being rotated to cause the whole semiconductor wafer W to be fluctuated and inclined. If a rotational accuracy of the semiconductor wafer W is worsened, a processing liquid, which has been supplied onto the semiconductor wafer W, does not spread uniformly over the surface of the semiconductor wafer W. As a result, the uniform process cannot be performed on the semiconductor wafer W. Further, the semiconductor wafer W being rotated is likely to be easily disengaged from the rollers 450. Therefore, it is necessary to increase the pressing forces applied from the rollers 450 to the semiconductor wafer W, thus accelerating wear of the rollers 450.
In addition, if the rotational accuracy of the semiconductor wafer W is worsened, an etching liquid (i.e., a processing liquid) enters not only a back surface and the peripheral portion of the semiconductor wafer W, but also an area where circuits (devices) are formed, and hence a portion, which is not to be processed, is processed by the etching liquid. Further, the processing liquid (e.g., the etching liquid or the cleaning liquid) gathers in clamp portions (recessed portions) of the rollers 450 and is then scattered in a direction tangent to the semiconductor wafer w or the rollers 450 as the semiconductor wafer W is rotated, thus causing contamination of the atmosphere and the semiconductor wafer W.